Fluid pressure springs

ABSTRACT

A fluid pressure spring (8), such as for opening the hatchback door of a vehicle, comprises a hollow cylinder (10) having a fixture (24) for pivotal connection to the hatchback door. A piston (30) is connected to a hollow piston rod (114) which carries a fixture (46) for pivotal connection to the vehicle body. The interior (40, 42) of the cylinder is filled with gas under pressure, and the gas extends into a chamber (54) within the piston rod via a bore (62). A free piston (50) within the hollow piston rod (14) is subjected to exterally applied hydraulic pressure via a pipe (20) connected to a second chamber (56) within the hollow piston rod (14). Controllable increase of this pressure moves the free piston (50) to augment the gas pressure within the spring and to increase its lifting force. In this way, a remote control can bused to unlatch the hatchback door and temporarily augment the gas pressure within the spring to cause the door automatically to lift from the fully closed position to the open position. If the gas pressure within the spring is insufficient by itself to raise the hatchback door to the open position, the augmenting hydraulic pressure can not only lift the hatchback door in this way but, when released, allows the door to close under gravity.

The invention relates to a gas spring connected to a closure member foran opening, the closure member being movable in a first direction from aclosed position to an open position and being movable in a seconddirection from the open position to the closed position, the closuremember moving against gravity in one said direction, the springcomprising a hollow cylinder, a piston slidable within the hollowcylinder and connected go a piston rod sealingly and slidingly extendingfrom the cylinder, the piston dividing the hollow cylinder into a firstchamber between the piston and one end of the cylinder and a second mainchamber through Which the piston rod extends, the first and second mainchambers containing gas under pressure which tends to displace thepiston rod from the cylinder, the gas spring being connected to theclosure member so that such displacement of the piston rod tends to movethe closure member in the said one direction, and externallycontrollable fluid pressure producing means for controllably augmentingthe pressure of the gas.

Such a gas spring is known from EP-A-0 379 864. In this knownarrangement, an external source of gas is connected directly to thefirst main chamber in the cylinder to vary the pressure for temperaturecompensation purposes. In the event of failure of the external pressuresource, there could be a complete loss of pressure within this mainchamber. The invention aims to deal with this problem.

In accordance with the invention, therefore, the known gas spring ischaracterised in that she piston rod is hollow, and by a second pistonsealingly slidable within the hollow interior of the piston rod anddividing the interior of the piston rod into first piston rod chamber incommunication with the second main chamber and a second piston rodchamber, and in that the externally controllable fluid pressureproducing means applies externally controllable fluid pressure to andwithin the second piston rod chamber for moving the second piston withinthe hollow interior of the piston rod so as to augment the gas pressurewithin the first piston rod chamber and the first and second mainchambers.

Fluid pressure springs embodying the invention, and for use in motorvehicles, will now be described, by way of example only, with referenceto the accompanying diagrammatic drawings in which:

FIG. 1 is a schematic diagram of part of a motor vehicle body, with ahatchback door whose opening and/or closing movement is controlled andassisted by one of the springs;

FIG. 2 is a cross-section through one or the springs;

FIG. 3 is a schematic diagram of one form of a hydraulic fluid systemfor use with the gas spring of FIG. 2; and

FIG. 4 is a schematic diagram of another hydraulic fluid system for usewith the gas spring of FIG. 2.

The fluid pressure springs to be described in more detail belowincorporate gas under pressure, the pressure of the gas beingcontrollable by hydraulic means.

Referring to FIG. 1, a motor vehicle of which part is indicateddiagrammatically at 5 has a horizontally pivotted hatchback door whichis shown in the raised or open position. In a manner to be explained,the opening and/or closing movement of the hatchback door 6 iscontrolled and assisted by a fluid spring 8. The spring (to be describedin more detail below) comprises a hollow cylindrical body 10 having aclosed end which is connected to the hatchback door 6 by a pivotal joint12. A piston rod 14 is sealingly slidable into and out of the oppositeend of the cylinder 10 and its distal end is connected by a secondpivotal joint 16 to the vehicle body 5.

The position of the fluid pressure spring 8 when the hatchback door 6 isclosed is shown dotted at 8A in FIG. 1, the hollow piston rod 14 nowbeing partially retracted within the cylindrical body 10.

The interior of the cylindrical body 10 contains gas under pressure. Inthe manner to be explained in more detail below, the pressure of the gascan be controllably altered by a hydraulic fluid arrangement. A sourceof adjustable hydraulic fluid pressure is indicated diagrammatically at18 and is connected by a flexible fluid pipe 20 to the interior of thespring 8 via a flexible pipe 20 and the hollow interior of the pistonrod 14. The position of the flexible pipe 20 when the hatchback door 6is closed is indicated diagrammatically at 20A in FIG. 1.

The spring 8 will now be described in more detail with reference to FIG.2. FIG. 2 shows the hollow cylindrical body 10 which is closed off atone end at 22, the end 22 supporting a fixture 24 which is connected tothe pivotal joint 12 (FIG. 1) and thence to the hatchback door 6. At itsopposite end, the cylindrical body 10 is provided with an aperturethrough which extends the hollow piston rod 14. The piston rod issupported by a guide 26. A seal 28 provides a fluid-tight seal aroundthe outside of the piston rod 14 and between the piston rod and thecylindrical body 10.

At its end inside the cylindrical body 10, the piston rod 14 is attachedto a piston 30. The piston 30 has an annular groove 32 in which ismounted a circular sealing ring 34 the diameter of which is less thanthe width of the groove 32. The piston has an axially directed groove 36in its periphery, a radially directed groove 37 and axially directedbores 38. The piston 30 and the sealing ring 34 thus divide the interiorof the cylindrical body 10 into two chambers 40 and 42. However, thesechambers can be interconnected, in a manner to be explained, via thegrooves 36 and 37 and the bores 38, depending on the position of thesealing ring 34 within the annular groove 32.

At its opposite end, the hollow piston rod 14 carries an end fitting 44supporting a fixture 46 which is in turn connected to the pivotal joint16 (FIG. 1) and thence to the vehicle body 5. A portion of the endfitting 44 extends into the interior of the piston rod 14 and is sealedto it by an annular seal 48. A free piston 50 is slidable within theinterior of the piston rod 14 and is sealed against the interior wall ofthe piston rod 14 by an annular sealing ring 52. The free piston 50 thusdivides the interior of the piston rod 14 into two chambers 54 and 56.

Chamber 56 is connected via a bore 58 within the end fitting 44 andthence to the hydraulic pipe 20 of FIG. 1.

At its inner end, the piston rod 14 has a fixed block 60 with a throughbore 62 interconnecting the chambers 42 and 54.

During manufacture, the hollow cylindrical body 10 is filled with gasunder pressure which therefore fills the chambers 40,42 and 54, but notchamber 56.

For explaining the operation of the fluid spring, the effect of thehydraulic fluid will initially be ignored. The operation of the springis therefore dependent on the gas pressure.

The gas pressure within the cylindrical body 10 will exert a force onthe piston rod 14 tending to expel the piston rod from the cylindricalbody. As the gas pressure drives the piston rod 14 and the piston 30 inthe direction outwardly of the cylindrical body 10, frictional forcebetween the interior wall of the cylindrical body 10 and the sealingring 34 shifts the sealing ring 34 to the left hand side (as viewed inFIG. 2) of the annular groove 32. A restricted passageway betweenchambers 40 and 42 is thus provided, through groove 36, groove 37 andbores 38, and this allows gas to transfer from chamber 42 to chamber 40as the piston moves.

The consequential outward movement of the piston rod 14 corresponds toopening of the hatchback door 6 (FIG. 1).

Movement of the piston rod 14 in the opposite direction, that is,inwardly of the cylindrical body 10, takes place in response to anexternal force applied to the piston rod, corresponding in this exampleto a closing force exerted on the hatchback door 6. As the piston rod isforced inwardly of the cylindrical body 10, the piston 30 movescorrespondingly. The frictional force between the interior wall of thecylindrical body 10 and the sealing ring 34 shifts the sealing ring 34to the right hand side (as viewed in FIG. 2) of the groove 32. There isnow a relatively large passageway connecting chambers 40 and 42 allowingrelatively rapid transfer of gas from chamber 40 to chamber 42, becausethe gas can now flow freely around the left hand side of, and thenunder, the sealing ring 34, the gas flow no longer being limited by thegroove 37. The gas pressure thus provides a relatively low opposingforce to the inward movement of the piston rod 14 and the piston 30.

The effect of the hydraulic fluid within chamber 56 will now beconsidered.

Basically, the hydraulic fluid system enables the gas pressure withinthe cylindrical body 10 to be externally adjusted. The application ofhydraulic fluid pressure into chamber 56, via the pipe 20 and the bore58, forces the free piston 50 to the left (as viewed in FIG. 2), thusapplying pressure to the gas within chamber 54 and thence to the gaswithin chambers 42 and 40 via the bore 62, the bore 38 and the grooves36 and 37. The resultant increase in gas pressure depends on thepressure exerted on the free piston 50 by the hydraulic fluid. Theaddition of the hydraulic fluid system to the spring 8 produces a numberof operational advantages as will now be described with particularreference to FIG. 1.

Referring to FIG. 1, and considering the situation when the hatchbackdoor 6 is closed, the gas pressure within spring 10 will not on its ownnormally be sufficient to open the hatchback (when its catch isreleased). This is because the mechanical arrangement is such that thegas pressure cannot overcome the weight of the hatchback. If thehatchback is lifted slightly, through a small angle, however, the torqueexerted on the hatchback door the gas spring now becomes greater thanthe torque exerted by the weight of the hatchback door, and the gaspressure can now lift the hatchback door to its fully open position andhold it in this position.

However, the addition of the hydraulic pressure system now enables thegas pressure to be controllably increased so that, for example, the gaspressure can be sufficient to open the hatchback door from its fullyclosed position (when it is unlatched). Thus, hydraulic fluid pressureis applied to chamber 56 (FIG. 2) through pipe 20 when the hatchbackdoor is unlatched, and increases the gas pressure within cylindricalbody 10 (chambers 40,42 and 54) to such an extent that the torqueexerted by the spring 8 can raise the hatchback door from its fullyclosed position. As soon as the hatchback door has moved through acertain angle from its fully closed position, the hydraulic fluidpressure can be released or reduced, because a lesser gas pressurewithin the spring is sufficient to raise the hatchback door towards, andto hold it in, the fully open position.

It is therefore possible for the opening of the hatchback door to becontrolled remotely such as by a telecontrol (e.g. operating by radio orinfra-red radiation). Such a telecontrol would be used to send a signalto a suitable electro-mechanical receiver within the vehicle which wouldunlatch the hatchback door and energise the hydraulic fluid system 18,thus causing the hatchback door to be raised in the manner justexplained.

In this case, closure of the hatchback door would take place manually.Thus, the hydraulic fluid pressure would be released or reduced and theweight of the hatchback door temporarily augmented by a manual downwardforce applied to the hatchback door to close it.

Instead, though, the operation could be modified so that the hatchbackdoor can be both raised and lowered by the use of the hydraulic system18 and, if desired, from a distance using a telecontrol.

In this mode, the initial gas pressure within the cylindrical body 10would be reduced so that, on its own (that is, when not augmented by thehydraulic fluid pressure), it is insufficient to hold the hatchback door6 open against its weight.

As before, the opening process involves the unlatching of the closedhatchback door and the application of hydraulic fluid pressure to thechamber 56 (FIG. 2). This hydraulic pressure increases the gas pressurewithin the cylindrical body 10 in the manner explained, until the gaspressure becomes sufficiently great to raise the hatchback door from thefully closed position and thence into the fully opened position. In thismode, though, the hydraulic fluid pressure within the chamber 56 wouldbe maintained continuously, in order to augment the gas pressure andthereby enable it to hold the hatchback door fully open.

When it is desired to close the hatchback door in this mode, a suitablesignal releases or reduces the hydraulic fluid pressure within chamber56. The gas pressure within the cylindrical body 10 is now reduced andthe weight of the hatchback door causes it to close, whereupon it may belatched. The signal may be produced by a force-sensitive transducerfitted to the spring which senses the closing force applied to thehatchback.

In this mode, the hatchback 6 may be provided with one or more proximitydetectors which sense for any obstruction during controlled closing oropening of the hatchback, and stop the movement in the event of any suchobstruction, such as by temporarily increasing or decreasing thehydraulic fluid pressure. Instead, or in addition, one or more positionsensors, responsive to the angle of the hatchback 6, can be used to stopthe opening movement of the hatchback (e.g. at a desired intermediateopen position) such as by decreasing the hydraulic pressure.

The spring shown in FIG. 2 is advantageous because the application ofthe hydraulic pressure by means of the movable separator 50 within thehollow piston rod 14 provides a compact arrangement. In addition, thearrangement provides a mechanical advantage as compared with anarrangement in which the piston rod 14 is not hollow and in which thehydraulic pressure acts directly on a separator slidable in the cylinder10.

FIGS. 3 and 4 show suitable hydraulic systems by way of example only.

FIG. 3 shows a hydraulic pump 70 which applies hydraulic fluid through apipe 72 to a controllable distributor 74. The distributor 74 isswitchable between a setting in which the pumped hydraulic fluid is fedinto a reservoir 76 and a setting in which the pumped hydraulic fluid isfed along pipe 20 (see FIG. 1) to the end unit 44 of FIG. 2 and thenceinto the chamber 56 of the spring 8. When the distributor 74 switchesthe pumped hydraulic fluid into the reservoir 76, so that the pipe 20 isno longer pressurised by the hydraulic fluid, the hydraulic fluid isreturned to a second reservoir 78 by the pressure exerted on the freepiston 50 by the gas within the spring. Reservoirs 76 and 78 areconnected by means not shown to feed back to a main reservoir from whichthe fluid is pumped by the pump 70.

The distributor 74 may be electrically or electronically controllable,such as by a telecontrol for the purpose already described.

In FIG. 4, a piston-cylinder unit 80 is provided, having a piston 82acting on hydraulic fluid within the closed off end 84 of the cylinder.This closed-off end is connected by the pipe 20 to the spring 8 andthence to the chamber 56. An electrically energisable force unit 86 isprovided which can be electrically energised to exert a force on thepiston 82 which in turn pressurises the hydraulic fluid and forces itinto the chamber 56. When the force unit 86 is de-energised, the forceexerted on the free piston 50 by the gas within the spring displaces thehydraulic fluid back into the closed-off end 84 of the piston-cylinderarrangement 80. Again, the force exerting unit 86 can be controlledelectrically or electronically such as by a suitable tele-control. It isadvantageous to use a piston-cylinder unit 80 having a relatively greatlength and a relatively small diameter. Such an arrangement enablesbetter control of the pressure.

In cold weather, the gas pressure within the cylindrical body 10 willtend to decrease. A temperature sensor can be incorporated to increasethe hydraulic pressure correspondingly so as to ensure that thehatchback opens correctly and also that it is held securely in the fullyopen position if the reduced gas pressure in cold weather isinsufficient on its own to do this. If the temperature sensor increasesthe hydraulic pressure in order to hold the hatchback 6 in the openposition, it may be difficult for the user to close the hatchback. Theuser may therefore have to release the hydraulic pressure manually tolower the hatchback. Alternatively, the spring can be fitted with aforce-sensitive transducer which senses the application of a closingforce to the hatchback and automatically releases the hydraulicpressure.

Although the foregoing description has referred to the use of hydraulicfluid pressure for controlling and temporarily augmenting the gaspressure within the spring 8, the pressure within chamber 56 can be acontrollable gas pressure instead, such as generated pneumatically.

What is claimed is:
 1. A gas spring in combination with and connected toa closure member for an opening, the closure member being movable in afirst direction from a closed position to an open position and beingmovable in a second direction from the open position to the closedposition, the closure member moving against gravity in one saiddirection, the spring comprisinga hollow cylinder, a piston slidablewithin the hollow cylinder and connected to a piston rod sealingly andslidingly extending from the cylinder, the piston rod being hollow anddefining a hollow interior, the piston dividing the hollow cylinder intoa first chamber between the piston and one end of the cylinder and asecond main chamber through which the piston rod extends, the first andsecond main chambers containing gas under pressure which ends todisplace the piston rod from the cylinder, means connecting the gasspring to the closure member so that such displacement of the piston rodtends to move the closure member in the said one direction, andexternally controllable fluid pressure producing means for controllablyaugmenting the pressure of the gas, and a second piston sealinglyslidable within the hollow interior of the piston rod and dividing theinterior of the piston rod into a first piston rod chamber incommunication with the second main chamber and a second piston rodchamber, the externally controllable fluid pressure producing meansapplying externally controllable fluid pressure to and within the secondpiston rod chamber for moving the second piston within the hollowinterior of the piston rod so as to augment the gas pressure within thefirst piston rod chamber and the first and second main chambers.
 2. Aspring according to claim 1, including a fluid passage extending throughthe piston rod from externally of the cylinder to the second piston rodchamber and for connection to the externally controllable fluid pressureproducing means.
 3. A spring according to claim 1, characterised thefirst and second main chambers are interconnected by means defining arestricted gas-flow passageway for enabling gas to transfer from thesecond main chamber to the first main chamber as the said displacementof the piston rod takes place, and to enable transfer of the gas fromthe first main chamber to the second main chamber when the piston rod ismoved inwardly of the cylinder in response to a force applied externallyto the piston rod in the direction opposite to the said one direction.4. A spring according to claim 3, including valve means automaticallyresponsive to the direction of movement of the piston within thecylinder to allow increased gas flow through the said passageway whenthe piston rod is moved inwardly of the cylinder.
 5. A spring accordingto claim 4, in which the valve means comprising sealing means forproviding a seal between the piston and the cylinder, the sealing meansbeing bodily movable in response to frictional force exerted on it bymovement of the piston, such bodily movement being between a position inwhich the sealing means provides partial blockage of the restrictedpassageway and a position in which it is relatively clear of therestricted passageway.
 6. A spring according to claim 1, includingcontrol means for controlling the magnitude of the externally appliedfluid pressure.
 7. A spring according to claim 6, in which the controlmeans is remotely operable.
 8. A spring according to claim 7, in whichthe control means is wirelessly operable.
 9. A spring according to claim1, including a force-sensitive transducer responsive to a force appliedmanually to the closure member in a direction opposite to the said onedirection for reducing the fluid pressure produced by the externallycontrollable fluid pressure producing means.
 10. A spring according toclaim 1 in which the pressure of the gas when not augmented isinsufficient to move the closure member in the said one direction froman initial position but is sufficient to move it in that direction froman intermediate position adjacent to but slightly displaced from theinitial position and is sufficient to hold the body in a final position,whereby the externally controllable fluid pressure means is operative toaugment the pressure of the gas sufficiently to enable it to move theclosure member from the initial position.
 11. A spring according toclaim 1, in which the pressure of the gas when not augmented isinsufficient to move the closure member in the said one direction,whereby the externally controllable fluid pressure means is operative toaugment the pressure of the gas sufficiently to move the closure memberin that direction from an initial position to a final position and tohold it in the final position and is operative to reduce the gaspressure to the unaugmented value to allow the closure member to returnto the initial position under gravity.
 12. A spring according to claim1, in which the closure member is a substantially horizontally hingedclosure member, on a vehicle.
 13. A spring according to claim 1,including sensing means responsive to movement of the closure member forcontrollably halting such movement if an obstruction is sensed.
 14. Aspring according to claim 13, in which the sensing means is a proximitydetector.
 15. A spring according to claim 13, in which the sensing meansis a position detector.
 16. A spring according to claim 13, in which thesensing means halts the movement of the closure member if an obstructionis detected by altering the fluid pressure produced by the fluidpressure producing means.
 17. A spring according to claim 1, including atemperature sensor for adjusting the fluid pressure produced by thefluid pressure producing means to compensate for changes in the gaspressure and the fluid pressure produced by temperature changes.
 18. Aspring according to claim 1, in which the externally controllable fluidpressure means comprises externally controllable hydraulic pressuremeans.
 19. A spring according to claim 1, in which the externallycontrollable fluid pressure means comprises externally controllable gaspressure means.